A month’s worth of rain could fall in less than an hour as thunderstorms batter the UK for three days in the wake of an early summer heatwave.
The Met Office has issued thunderstorm warnings for Thursday, Friday and Saturday, with the entire country covered by a yellow warning on Friday when the heaviest rain is expected.
Up to 50mm (2ins) of rain could fall in less than an hour in places, bringing a risk of flooding, and lightning and hail could also pose a danger to life after the hottest temperatures of the year so far, according to forecasters.
The Met Office said thunderstorms will roll into parts of the western UK late on Thursday afternoon and into the evening before a larger area of storms moves northeastwards.
Heavy showers and thunderstorms will break out across the UK on Friday – when the entire country will be under a severe weather warning – and linger into Saturday morning in parts of Scotland.
Health warnings have been issued for the heatwave which will send temperatures soaring to about 33C in the south of England on Wednesday and Thursday.
Coronavirus “shielders”, the elderly, very young children and people with health conditions are most at risk.
UV levels are expected to hit nine – or about as high as it can get in the UK. Pollen levels also remain “very high”.
Forecasters and medics have urged people to take extra precautions to stay safe in the sun, and a water safety warning has been issued as people go for a dip in the sea, lakes, streams and swimming pools to cool off.
On Tuesday night, emergency services rushed to the River Thames in Cookham, Berkshire amid reports a man was missing after going into the water amid the warm weather. He is feared to have drowned.
Two thunderstorm warnings have been issued by the Met Office – one for the western side of the UK and the other for the rest of the country.
These are the areas they cover and the potential impacts which could pose a danger to life.
Thursday 4pm to Friday 9am
This warning covers the entire western side of the UK, bringing a risk of flooding and a chance that some communities could become cut off by submerged roads.
Travel could be disrupted and power cuts could occur.
The Met Office said: “Thunderstorms may develop across parts of western UK late on Thursday afternoon and into the evening.
“A larger area of thunderstorms is then expected to move northeastwards overnight into Friday.
“Many places will miss the worst of the storms but where they do occur torrential downpours could bring 30-40 mm rain in less than two hours.
“Lightning and hail are also likely to be additional hazards.”
Friday 12pm to Saturday 6am
The heaviest rain is expected in this warning area, which could also see flooding, communities being cut off if roads are under water, travel disruption and power cuts.
As much as 50mm of rain could fall in less than 60 minutes. Some places average less than 50mm for the entire month of June.
The Met Office said: “Heavy showers and thunderstorms are likely to break out on Friday afternoon and evening.
“Many places will miss the storms, but where they do occur, torrential downpours could bring 30-50mm rain in a hour, with hail and lightning.
“The storms will slowly clear northeastwards on Friday night, perhaps not clearing northeast Scotland until Saturday morning.”
A level three or amber heat warning – the second highest level – has been issued for the Midlands amid concerns the heatwave could lead to dangerous situations or further water tragedies. The rest of England was under a level two or yellow warning.
Temperatures will soar above 30C in the south and people will be at risk of heat-related illness.
Met Office meteorologist Alex Burkill said UV levels will be “reaching eight across many places and will be reaching nine across parts of Devon and Cornwall tomorrow.
He said: “That’s about as high as it gets really in the UK. The sun is as strong as it gets at the moment because we’re so close to the solstice.
“We’ve got peak sun strength, clear skies, plenty of sunshine – it’s the perfect ingredients for high UV.”
Mr Burkill advised anyone outside for prolonged periods of time on Wednesday and Thursday to take measures to protect themselves.
Shoppers have also been advised to be aware they could be forced to spend extra time in the sun as a result of social distancing measures.
Dr Lynn Thomas, medical director at St John Ambulance, said: “You could end up in the sun for longer than expected on what would normally be a quick journey, such as queuing to enter the supermarket, so you should be prepared to look after yourself and others.”
She added: “Heat exhaustion and heatstroke are two of the most serious problems that can develop when the mercury soars but by being prepared you can spot the early warning signs, such as headache and dizziness.”
London Fire Brigade (LFB) has warned people not to have barbecues on dry grass, not to drop cigarettes or matches, and not to leave rubbish such as glass bottles lying around amid a risk they could start fires.
LFB Deputy Cmmissioner Richard Mills said: “Barbecuing on dry grass is thoughtless and reckless and can easily be the cause of a significant fire, which isn’t something you want on your conscience.
The public is also being reminded to take care around water throughout the summer, amid concerns people might be tempted to take a dip to cool down.
“But we are going to beat it tomorrow and the day after,” Mr Burkill said.
He predicted temperatures would edge towards 33C as we experience “lots of hot and sunny weather through the next couple of days”.
The forecaster added: “The heat is going to be quite widespread, even across parts of Scotland we could be looking at highs of 26 or 27.”
“The nights are going to be uncomfortably hot as well, so people who are susceptible to the heat will struggle.”
In the warmest places, temperatures will drop into the high 20s on Friday and then into the low 20s on Saturday after unsettled weather hits.
Tuesday was not quite the hottest day of the year, as the 28.6C recorded at Heathrow Airport and Kew Gardens fell short of the 28.9C recorded at the end of May.
UK five-day weather forecast
Rain across parts of Northern Ireland and Scotland slowly dying out, cloud breaking to allow some brightness this afternoon.
Hot and sunny elsewhere, with sea breezes keeping coasts a little cooler.
Dry and warm with clear skies for many.
Muggy in towns and cities.
A few isolated thunderstorms are possible across Scotland.
Hot and sunny across most parts.
A few thunderstorms perhaps developing across Scotland during the afternoon, then a risk of more widespread thunderstorms across the southwest later.
Friday to Sunday
Hot in the east on Friday but a thundery breakdown during the day will lead to fresher, breezier conditions developing over the weekend with showers or longer spells of rain.
UK long-range weather forecast
Here is what the Met Office is predicting between Sunday and July 7: “The end of June will see a change of weather for much of the UK as it becomes cooler, breezier and more changeable.
“This will bring a chance of showers, especially for western parts, and also some more persistent rain, most likely through central and southern areas.
“There will however still be some drier and sunny interludes.
“This changeable weather continues into July with sunshine, showers and perhaps some longer spells of rain possible for many.
“The rain however looks to be mainly in the northwest where it may be cooler also.
“The best of any drier and brighter weather will be across the south and east of the UK.
“Breezy conditions continuing, particularly for the north.
“Temperatures mostly around average for the time of year.”